The present invention relates to a hybrid drive for a motor vehicle with an internal combustion engine and an electric motor.
A hybrid drive is defined as a combination of various drive principles or energy sources for the task of driving during use. The use of hybrid drives, which exhibit an internal combustion engine and an electric motor, is also increasing in the construction of modern motor vehicles. By operating the internal combustion engine in a very good efficiency range, it is possible to save fuel while driving. However, the motor vehicle has not only the electric motor, but also other auxiliary units, such as an air conditioner compressor, a servo pump or a fan, all of which have either their own electric motor or are connected to the crankshaft of the internal combustion engine for the purpose of driving via a belt drive. However, the latter variant is problematic in hybrid motor vehicles, since in the case of a pure electric drive, the internal combustion engine is disengaged, thus eliminating a drive of the auxiliary units by means of the crankshaft and the belt drive. Therefore, hybrid motor vehicles require that an alternative drive source is assigned to each auxiliary unit. However, this feature is complex in design and expensive. Especially when electric motors are used as the drive sources of the auxiliary units, there is an increase not only in the complexity of the control and wiring, but also in the complexity of the management of the electric energy budget of the vehicle.
The present invention deals with the problem of providing an improved embodiment of a hybrid drive for a motor vehicle, so that it is possible to design and operate in a simple and economical manner the auxiliary units, disposed in the motor vehicle, when the internal combustion engine is disengaged.
The invention solves this problem by way of a hybrid drive for a motor vehicle, including an internal combustion engine, an electric motor, at least one auxiliary unit, and a belt/chain drive by which the internal combustion engine, the electric motor, and the at least one auxiliary unit are connected together in a drive relationship, in which the internal combustion engine and the electric motor have respective drive elements with unidirectional freewheeling devices for the belt/chain drive.
Advantageous embodiments are also claimed.
According to the invention, the mechanical energy generated by the electric motor is used for driving the auxiliary units. To this end, an internal combustion engine and an electric motor of the hybrid drive and at least one auxiliary unit are connected together in a drive relationship by means of a belt/chain drive. In so doing, both the internal combustion engine and the electric motor have a respective drive element with a unidirectional freewheeling device for the belt/chain drive. Therefore, in a purely internal combustion engine drive state, the belt/chain drive is driven by the internal combustion engine and transforms the mechanical movement into a torque at the electric motor as well as a torque at the auxiliary unit. As a result, the auxiliary unit is driven, and at the same time a vehicle battery is charged up, by means of the electric motor, which acts as a generator. When the vehicle battery is totally charged, the drive element at the electric motor can be shifted into the free running mode, so that despite the rotating crankshaft, the electric motor no longer rotates concomitantly. In contrast, in the electric motor drive state, the freewheeling device at the drive element of the crankshaft of the internal combustion engine is actuated, so that the electric motor drives only said at least one auxiliary unit, whereas the crankshaft does not rotate.
In an advantageous further development, the freewheeling device of the drive element of the electric motor is closed up to a limit speed vlimit of the belt/chain drive and is opened at a higher speed, whereas the freewheeling device of the drive element of the internal combustion engine is closed after the limit speed vlimit and is opened at a lower speed. In this way, it is possible to establish an exactly defined speed at the auxiliary units, where the speed is speed-independent of the speed of the electric motor and/or the speed of the internal combustion engine. This feature makes it possible to design the auxiliary units specifically in terms of the necessary power output. Thus, it is possible to achieve both a reduction in weight and cost of the auxiliary units. Thus, a design of the auxiliary units with respect to both adequate power output at minimum speed and as a high speed-fixed auxiliary unit can be dispensed with. In particular, mechanical stress on the auxiliary units can also be limited, so that the auxiliary units have to be designed in essence only with respect to a constant operating state/power output state and no longer need to cope or rather cover, as in the past, varying operating/power output states.
It is desirable to provide the drive element of the internal combustion engine with a clutch and/or a brake, which enables a belt/chain speed that is independent of the speed of the drive element. Thus, it is possible to set a constant belt/chain speed, which corresponds preferably to an ideal drive speed of the auxiliary unit that is driven with the belt/chain drive, even at high speeds of the crankshaft of the internal combustion engine. In so doing, it is conceivable that the electric motor drives the belt/chain drive in a lower speed range, whereas the internal combustion engine drives the belt/chain drive at higher speeds, at which the freewheeling device of the drive element, arranged at the electric motor, is already activated. If the speed of the crankshaft in the internal combustion engine continues to increase, the clutch and/or the brake prevents the overshooting of a predefined belt/chain speed. This measure also eliminates the need for a high speed-fixed design of the auxiliary units, thus making it possible to manufacture them more economically.
Other important features and advantages of the invention follow from the dependent claims, the drawings and the associated description of the figures with reference to the drawings.
The aforementioned features and those mentioned below can be applied not only in the specified combination, but also in other combinations or alone without departing from the scope of the present invention.
Preferred embodiments of the invention are depicted in the drawings and are explained in detail in the following description. Identical reference numerals and symbols refer to the same or similar or functionally identical components.